Abstract
Rap1 is a small, Ras-like GTPase that was first identified as a protein that could suppress the oncogenic transformation of cells by Ras1. Rap1 is activated by several extracellular stimuli2,3,4,5,6,7 and may be involved in cellular processes such as cell proliferation8, cell differentiation4, T-cell anergy2 and platelet activation7. At least three different second messengers, namely diacylglycerol, calcium and cyclic AMP5,6,7,8,9 are able to activate Rap1 by promoting its release of the guanine nucleotide GDP and its binding to GTP. Here we report that activation of Rap1 by forskolin and cAMP occurs independently of protein kinase A (also known as cAMP-activated protein kinase). We have cloned the gene encoding a guanine-nucleotide-exchange factor (GEF) which we have named Epac (exchange protein directly activated by cAMP). This protein contains a cAMP-binding site and a domain that is homologous to domains of known GEFs for Ras and Rap1. Epac binds cAMP in vitro and exhibits in vivo and in vitro GEF activity towards Rap1. cAMP strongly induces the GEF activity of Epac towards Rap1 both in vivo and in vitro. We conclude that Epac is a GEF for Rap1 that is regulated directly by cAMP and that Epac is a new target protein for cAMP.
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Acknowledgements
We thank F. W. Herberg for the GST-RIα subunit of PKA, M. Gottesman for CHO10001/10248 cells, B. M. T. Burgering for discussions and for reading the manuscript and the rest of our colleagues for continuous support and discussions. J.deR. and M.H.G.V. were supported by the Council of Earth and Life Sciences of the Netherlands Organization for Scientific Research, F.J.T.Z. by the Dutch Cancer Society and R.H.C. by the EG.
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de Rooij, J., Zwartkruis, F., Verheijen, M. et al. Epac is a Rap1 guanine-nucleotide-exchange factor directly activated by cyclic AMP. Nature 396, 474–477 (1998). https://doi.org/10.1038/24884
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DOI: https://doi.org/10.1038/24884
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